Semiconductor structure and manufacturing method thereof

ABSTRACT

A semiconductor structure includes a substrate, a first gate structure, a first spacer, a source/drain structure, a conductor, and a contact etch stop layer. The first gate structure is present on the substrate. The first spacer is present on at least one sidewall of the first gate structure, in which the first spacer has a top portion and a bottom portion between the top portion and the substrate. The source/drain structure is present adjacent to the bottom portion of the first spacer. The conductor is electrically connected to the source/drain structure. The protection layer is present at least between the conductor and the top portion of the first spacer. The contact etch stop layer is present at least partially between the conductor and the bottom portion of the first spacer while absent between the protection layer and the top portion of the first spacer.

PRIORITY CLAIM AND CROSS-REFERENCE

This application claims priority to U.S. Provisional Application Ser. No. 62/269,851, filed Dec. 18, 2015, which is herein incorporated by reference.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications, such as personal computers, cell phones, digital cameras, and other electronic equipment, as examples. The semiconductor industry continues to improve the integration density of various electronic components (e.g., transistors, diodes, resistors, capacitors, etc.) by continual reductions in minimum feature size, which allow more components to be integrated into a given area.

The word “interconnection” in integrated circuits means conductive lines which connect the various electronic components. The interconnecting conductive lines are separated from the substrate by insulating layers, except on the contact area. As feature densities increase, the widths of the conductive lines and the spacing between the conductive lines of interconnect structures also scale smaller.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIGS. 1-10 are cross-sectional views of a method for manufacturing a semiconductor structure at various stages in accordance with some embodiments of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

The singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising”, or “includes” and/or “including” or “has” and/or “having” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof.

It will be understood that when an element is referred to as being “on” another element, it can be directly on the other element or intervening elements may be present therebetween. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by the person having ordinary skill in the art. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

FIGS. 1-10 are cross-sectional views of a method for manufacturing a semiconductor structure at various stages in accordance with some embodiments of the present disclosure.

Reference is made to FIG. 1. A semiconductor structure is formed. The semiconductor structure includes a substrate 110, gate structures 121 s, 121 b, 123 s, and 123 b, and source/drain structures 130 s and 130 b. The gate structures 121 s, 121 b, 123 s, and 123 b are present on the substrate 110. The source/drain structure 130 s is present on the substrate 110 and adjacent to the gate structures 121 s and 123 s, and the source/drain structure 130 b is present on the substrate 110 and adjacent to the gate structures 121 b and 123 b. In other words, the source/drain structure 130 s is present between the gate structures 121 s and 123 s, and the source/drain structure 130 b is present between the gate structures 121 b and 123 b. It is note that the numbers of the gate structures 121 s, 121 b, 123 s, and 123 b and the number of the source/drain structures 130 s and 130 b are illustrative and should not limit various embodiments of the present disclosure. The numbers of the gate structures 121 s, 121 b, 123 s, and 123 b and the source/drain structures 130 s, and 130 b may vary according to actual situations.

Specifically, the source/drain structure 130 s is narrower than the source/drain structure 130 b. That is, the gate structures 121 s and 123 s and the source/drain structure 130 s belong to at least one semiconductor device having at least one narrower source/drain contact, and the gate structures 121 b and 123 b and the source/drain structure 130 b belong to at least one semiconductor device having at least one wider source/drain contact.

In some embodiments, the substrate 110 may be made of a semiconductor material and may include, for example, a graded layer or a buried oxide therein. In some embodiments, the substrate 110 includes bulk silicon that may be undoped or doped (e.g., p-type, n-type, or combinations thereof). Other materials that are suitable for semiconductor device formation may be used. For example, germanium, quartz, sapphire, and glass could alternatively be used for the substrate 110. Alternatively, the substrate 110 may be an active layer of a semiconductor-on-insulator (SOI) substrate or a multi-layered structure, such as a silicon-germanium layer formed on a bulk silicon layer.

In some embodiments, at least one stack of a gate dielectric layer, a diffusion barrier layer, a metal layer, a block layer, a wetting layer, and filling metal form at least one of the gate structures 121 s, 121 b, 123 s, and 123 b. In other words, at least one of the gate structures 121 s, 121 b, 123 s, and 123 b may include the stack of the gate dielectric layer, the diffusion barrier layer, the metal layer, the block layer, the wetting layer, and the filling metal.

In some embodiments, the gate dielectric layer includes an interfacial layer (IL, the lower part of the gate dielectric layer), which is a dielectric layer. In some embodiments, the IL includes an oxide layer, such as a silicon oxide layer, which may be formed through thermal oxidation of the substrate 110, chemical oxidation of the substrate 110, or a deposition step. The gate dielectric layer may also include a high-k dielectric layer (the upper part of the gate dielectric layer) including a high-k dielectric material, such as hafnium oxide, lanthanum oxide, aluminum oxide, or combinations thereof. The dielectric constant (k-value) of the high-k dielectric material is higher than about 3.9, and may be higher than about 7, and sometimes as high as about 21 or higher. The high-k dielectric layer is overlying, and may contact, the IL.

In some embodiments, the diffusion barrier layer includes TiN, TaN, or combinations thereof. For example, the diffusion barrier layer may include a TiN layer (the lower part of the diffusion barrier layer) and a TaN layer (the upper part of the diffusion barrier layer) over the TiN layer.

When one of the gate structures 121 s, 121 b, 123 s, and 123 b forms an n-type metal-oxide-semiconductor (MOS) device, the metal layer is in contact with the diffusion barrier layer. For example, in the embodiments in which the diffusion barrier layer includes a TiN layer and a TaN layer, the metal layer may be in physical contact with the TaN layer. In alternative embodiments in which one of the gate structures 121 s, 121 b, 123 s, and 123 b forms a p-type MOS device, an additional TiN layer is formed between, and in contact with, the TaN layer (in the diffusion barrier layer) and the overlaying metal layer. The additional TiN layer provides the work function suitable for the pMOS device, which work function is higher than the mid-gap work function (about 4.5 eV) that is in the middle of the valance band and the conduction band of silicon. The work function higher than the mid-gap work function is referred to as a p-work function, and the respective metal having the p-work function is referred to as a p-metal.

The metal layer provides the work function suitable for the nMOS device, which work function is lower than the mid-gap work function. The work function lower than the mid-gap work function is referred to as an n-work function, and the respective metal having the n-work function may be referred to as an n-metal. In some embodiments, the metal layer is an n-metal having a work function lower than about 4.3 eV. The work function of the metal layer may also be in a range from about 3.8 eV to about 4.6 eV. The metal layer may include titanium aluminum (TiAl) (which may include, or free from or substantially free from other elements) in accordance with some embodiments. The formation of the metal layer may be achieved through physical vapor deposition (PVD). In accordance with some embodiments of the present disclosure, the metal layer is formed at room temperature (for example, from about 20° C. to about 25° C.). In alternative embodiments, the metal layer is formed at an elevated temperature higher than the room temperature, for example, higher than about 200° C.

The block layer may include TiN in some embodiments. The block layer may be formed using atomic layer deposition (ALD).

The wetting layer has an ability to adhere (and wet) the subsequently formed filling metal during the reflow of the filling metal. In some embodiments, the wetting layer is a cobalt layer, which may be formed using atomic layer deposition (ALD) or chemical vapor deposition (CVD).

The filling metal may include aluminum, an aluminum alloy (e.g., titanium aluminum), tungsten, or copper, which may also be formed using physical vapor deposition (PVD), chemical vapor deposition (CVD), or the like. The filling metal may be reflowed. The formation of the wetting layer improves the wetting of the filling metal to the underlying layers.

The source/drain structures 130 s and 130 b may be formed by doping impurities into active semiconductor fins, which are formed by, for example, patterning and etching the substrate 110 using photolithography techniques. In some embodiments that the resulting MOS devices are nMOS devices, n-type impurities such as phosphorous or arsenic may be doped in the source/drain structures 130 s and 130 b. In some other embodiments that the resulting MOS devices are pMOS devices, p-type impurities such as boron or BF₂ may be doped in the source/drain structures 130 s and 130 b.

Alternatively, the source/drain structures 130 s and 130 b may be formed by, for example, epitaxial growth. In these embodiments, the source/drain structures 130 s and 130 b may function as source/drain stressors to enhance carrier mobility of the semiconductor devices and the device performance. The source/drain structures 130 s and 130 b may be formed using a cyclic deposition and etching (CDE) process. The CDE process includes an epitaxial deposition/partial etch process and repeating the epitaxial deposition/partial etch process at least once.

In some embodiments that the resulting MOS devices are nMOS devices, the source/drain structures 130 s and 130 b may be n-type epitaxy structures. In some embodiments that the resulting MOS devices are pMOS devices, the source/drain structures 130 s and 130 b may be p-type epitaxy structures. The n-type epitaxy structures may be made of SiP, SiC, SiPC, Si, III-V compound semiconductor materials or combinations thereof, and the p-type epitaxy structures may be made of SiGe, SiGeC, Ge, Si, III-V compound semiconductor materials, or combinations thereof. During the formation of the n-type epitaxy structures, n-type impurities such as phosphorous or arsenic may be doped with the proceeding of the epitaxy. For example, when the n-type epitaxy structures include SiP or SiC, n-type impurities are doped. Moreover, during the formation of the p-type epitaxy structures, p-type impurities such as boron or BF₂ may be doped with the proceeding of the epitaxy. For example, when the p-type epitaxy structures include SiGe, p-type impurities are doped. The epitaxy processes include CVD deposition techniques (e.g., vapor-phase epitaxy (VPE) and/or ultra-high vacuum CVD (UHV-CVD)), molecular beam epitaxy, and/or other suitable processes. The source/drain structures 130 s and 130 b may be in-situ doped. If the source/drain structures 130 s and 130 b are not in-situ doped, a second implantation process (i.e., a junction implant process) is performed to dope the source/drain structures 130 s and 130 b. One or more annealing processes may be performed to activate the source/drain structures 130 s and 130 b. The annealing processes include rapid thermal annealing (RTA) and/or laser annealing processes.

In addition, spacers 141 s are present on sidewalls of the gate structure 121 s, spacers 143 s are present on sidewalls of the gate structure 123 s, spacers 141 b are present on sidewalls of the gate structure 121 b, and spacers 143 b are present on sidewalls of the gate structure 123 b. In some embodiments, at least one of the spacers 141 s, 141 b, 143 s, and 143 b include one or more layers, including silicon nitride, silicon oxynitride, silicon oxide, or other dielectric materials. The available formation methods include plasma enhanced chemical vapor deposition (PECVD), low-pressure chemical vapor deposition (LPCVD), sub-atmospheric chemical vapor deposition (SACVD), and other deposition methods.

Reference is made to FIG. 2. A contact etch stop layer (CESL) 191 is formed on the top surfaces of the gate structures 121 s, 121 b, 123 s, and 123 b, the spacers 141 s, 141 b, 143 s, and 143 b, and the source/drain structures 130 s, and 130 b and the side surfaces of the spacers 141 s, 141 b, 143 s, and 143 b. The CESL 191 may include, for example, silicon nitride or the like. The CESL 191 may be formed using chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), other suitable processes, or combinations thereof.

Then, a dielectric layer 150 is formed on the CESL 191. At least a portion of the dielectric layer 150 is present between the spacers 141 s and 143 s and on the source/drain structure 130 s, and at least a portion of the dielectric layer 150 is present between the spacers 141 b and 143 b and on the source/drain structure 130 b. The dielectric layer 150 is an interlayer dielectric (ILD) layer. The dielectric layer 150 is made of a dielectric material, such as silicon oxide, silicon nitride, silicon oxynitride, or combinations thereof. In some embodiments, the dielectric layer 150 is made of a low-κ dielectric material to improve resistive-capacitive (RC) delay. The dielectric constant of the low-κ dielectric material is lower than that of silicon dioxide (SiO₂). One approach to reduce the dielectric constant of a dielectric material is to introduce carbon (C) or fluorine (F) atoms. For example, in SiO₂ (κ=3.9), the introduction of C atoms to form hydrogenated carbon-doped silicon oxide (SiCOH) (κ is between 2.7 and 3.3) and the introduction of F atoms to form fluorosilicate glass (FSG) (κ is between 3.5 and 3.9) reduces its dielectric constant. In some embodiments, the low-κ dielectric material is, for example, nanopore carbon doped oxide (CDO), black diamond (BD), a benzocyclobutene (BCB) based polymer, an aromatic (hydrocarbon) thermosetting polymer (ATP), hydrogen silsesquioxane (HSQ), methyl silsesquioxane (MSQ), poly-arylene ethers (PAE), diamond-like carbon (DLC) doped with nitrogen, or combinations thereof. The dielectric layer 150 is formed by, for example, chemical vapor deposition (CVD), spin coating, or combinations thereof.

As shown in FIG. 2 and FIG. 3, the CESL 191 and the dielectric layer 150 above the gate structures 121 s, 121 b, 123 s, and 123 b are removed through a removal process. In some embodiments, the CESL 191 and the dielectric layer 150 above the gate structures 121 s, 121 b, 123 s, and 123 b are removed by a chemical mechanical polishing (CMP) process. After the CMP process, a portion of the residual dielectric layer 150 is present on the source/drain structure 130 s and between the gate structures 121 s and 123 s, and a portion of the residual dielectric layer 150 is present on the source/drain structure 130 b and between the gate structures 121 b and 123 b. A portion of the residual CESL 191 is present between the portion of the dielectric layer 150 on the source/drain structure 130 s and the spacer 141 s, between the portion of the dielectric layer 150 on the source/drain structure 130 s and the spacer 143 s, and between the portion of the dielectric layer 150 on the source/drain structure 130 s and the source/drain structure 130 s. A portion of the residual CESL 191 is present between the portion of the dielectric layer 150 on the source/drain structure 130 b and the spacer 141 b, between the portion of the dielectric layer 150 on the source/drain structure 130 b and the spacer 143 b, and between the portion of the dielectric layer 150 on the source/drain structure 130 b and the source/drain structure 130 b.

Reference is made to FIG. 4. Upper portions of the residual dielectric layer 150 are removed, such that the portion of the dielectric layer 150 and the portion of the CESL 191 on the source/drain structure 130 s form a recess 151 s, and the portion of the dielectric layer 150 and the portion of the CESL 191 on the source/drain structure 130 b form a recess 151 b. At least portions of the CESL 191 are exposed by the recesses 151 s and 151 b. The upper portions of the residual dielectric layer 150 are removed by etching. The etching of the dielectric layer 150 may be dry etching, such as reactive ion etching (RIE), plasma enhanced (PE) etching, or inductively coupled plasma (ICP) etching. In some embodiments, when the dielectric layer 150 is made of silicon oxide, fluorine-based RIE can be used to form the recesses 151 s and 151 b. The gas etchant used to dry etch the dielectric layer 150 is, for example, CF₄/O₂.

Reference is made to FIG. 5. Upper portions of the CESL 191 are removed. Top portions of the spacers 141 s and 143 s adjacent to the recess 151 s are rounded to be rounded top corners, and top portions of the spacers 141 b and 143 b adjacent to the recess 151 b are rounded to be rounded top corners. Specifically, the removing and the corner rounding are performed by trimming. More specifically, the trimming may be dry etching, such as reactive ion etching (RIE), plasma enhanced (PE) etching, or inductively coupled plasma (ICP) etching, or selective wet etching, which is a chemical etching process. A wet etching solution may include a hot phosphoric acid solution.

Reference is made to FIG. 6. A protection layer 160 is formed on the top surfaces of the gate structures 121 s, 121 b, 123 s, and 123 b, sidewalls of the recesses 151 s and 151 b (i.e., the rounded top corners of the spacers 141 s, 141 b, 143 s, and 143 b and the exposed CESL 191), and bottom surfaces of the recesses 151 s and 151 b (i.e., top surfaces of the portion of the dielectric layer 150 on the source/drain structure 130 s and the portion of the dielectric layer 150 on the source/drain structure 130 b). The protection layer 160 may include, for example, silicon nitride, silicon oxynitride, or the like. The protection layer 160 may be formed using atomic layer deposition (ALD), other suitable processes, or combinations thereof.

In FIG. 7, a dielectric layer 170 is formed on the protection layer 160. The dielectric layer 170 is an interlayer dielectric (ILD) layer. The dielectric layer 170 is made of a dielectric material, such as silicon oxide, silicon nitride, silicon oxynitride, or combinations thereof. In some embodiments, the dielectric layer 170 is made of a low-K dielectric material to improve resistive-capacitive (RC) delay. In some embodiments, the low-K dielectric material is, for example, hydrogenated carbon-doped silicon oxide (SiCOH), fluorosilicate glass (FSG), nanopore carbon doped oxide (CDO), black diamond (BD), a benzocyclobutene (BCB) based polymer, an aromatic (hydrocarbon) thermosetting polymer (ATP), hydrogen silsesquioxane (HSQ), methyl silsesquioxane (MSQ), poly-arylene ethers (PAE), diamond-like carbon (DLC) doped with nitrogen, or combinations thereof. The dielectric layer 170 is formed by, for example, chemical vapor deposition (CVD), spin coating, or combinations thereof.

Reference is made to FIG. 7 and FIG. 8. A hole 171 s is formed in the dielectric layers 150 and 170 to expose the source/drain structure 130 s, and a portion of the protection layer 160 on the bottom surface of the recess 151 s is removed when the hole 171 s is formed. A hole 171 b is formed in the dielectric layers 150 and 170 to expose the source/drain structure 130 b, and a portion of the protection layer 160 on the bottom surface of the recess 151 b is removed when the hole 171 b is formed. At least portions of the protection layer 160 are exposed by the holes 171 s and 171 b. The holes 171 s and 171 b are formed by a photolithography and etching process. The photolithography and etching process includes photoresist application, exposure, developing, etching, and photoresist removal. A photoresist is applied onto the dielectric layer 170 by, for example, spin coating. The photoresist is then prebaked to drive off excess photoresist solvent. After prebaking, the photoresist is exposed to a pattern of intense light.

The intense light is, for example, a G-line with a wavelength of about 436 nm, an I-line with a wavelength of about 365 nm, a krypton fluoride (KrF) excimer laser with a wavelength of about 248 nm, an argon fluoride (ArF) excimer laser with a wavelength of about 193 nm, a fluoride (F₂) excimer laser with a wavelength of about 157 nm, or combinations thereof. A space between the final lens of the exposure tool and the photoresist surface may be filled with a liquid medium that has a refractive index greater than one during the exposure to enhance the photolithography resolution. The exposure to light causes a chemical change that allows some of the photoresist soluble in a photographic developer.

Then, a post-exposure bake (PEB) may be performed before developing to help reduce standing wave phenomena caused by the destructive and constructive interference patterns of the incident light. The photographic developer is then applied onto the photoresist to remove the some of the photoresist soluble in the photographic developer. The remaining photoresist is then hard-baked to solidify the remaining photoresist.

At least one portion of the dielectric layer 170 which is not protected by the remaining photoresist is etched to form the holes 171 s and 171 b. The etching of the dielectric layer 170 may be dry etching, such as reactive ion etching (RIE), plasma enhanced (PE) etching, or inductively coupled plasma (ICP) etching. In some embodiments, when the dielectric layer 170 is made of silicon oxide, fluorine-based RIE can be used to form the holes 171 s and 171 b. The gas etchant used to dry etch the dielectric layer 170 is, for example, CF₄/O₂.

After the holes 171 s and 171 b are formed, the photoresist is removed from the dielectric layer 170 by, for example, plasma ashing, stripping, or combinations thereof. Plasma ashing uses a plasma source to generate a monatomic reactive species, such as oxygen or fluorine. The reactive species combines with the photoresist to form ash which is removed with a vacuum pump. Stripping uses a photoresist stripper, such as acetone or a phenol solvent, to remove the photoresist from the dielectric layer 170.

In addition, after the holes 171 s and 171 b are formed, at least portions of the residual dielectric layer 150 are present on sidewalls of the holes 171 s and 171 b. Specifically, the portion of the residual dielectric layer 150 on the sidewall of the hole 171 s is present on the spacers 141 s and 143 s on the sidewalls of the gate structures 121 s and 123 s, and the portion of the residual dielectric layer 150 on the sidewall of the hole 171 b is present on the spacers 141 b and 143 b on the sidewalls of the gate structures 121 b and 123 b.

Reference is made to FIG. 9. A conductive layer 180 overfills the holes 171 s and 171 b. The conductive layer 180 is made of metal, such as copper (Cu), aluminum (Al), tungsten (W), nickel (Ni), cobalt (Co), titanium (Ti), platinum (Pt), tantalum (Ta), or combinations thereof. The conductive layer 180 is formed by, for example, electrochemical deposition, physical vapor deposition (PVD), chemical vapor deposition (CVD), or combinations thereof.

Then, as shown in FIG. 9 and FIG. 10, the excess conductive layer 180 outside of the holes 171 s and 171 b is removed. The excess conductive layer 180 outside of the holes 171 s and 171 b is removed through a removal process. In some embodiments, the conductive layer 180 over burden is removed by a chemical mechanical polishing (CMP) process. In some embodiments, when the conductive layer 180 is made of copper (Cu), the CMP slurry is made of, for example, a mixture of suspended abrasive particles, an oxidizer, and a corrosion inhibitor, and the CMP slurry is acidic. After the CMP process, a conductor 181 s (the conductive layer 180) is formed in the hole 171 s, and a conductor 181 b (the conductive layer 180) is formed in the hole 171 b. The conductor 181 s is electrically connected to the source/drain structure 130 s, and the conductor 181 b is electrically connected to the source/drain structure 130 b. A portion of the protection layer 160 is present between the conductor 181 s and the spacer 141 s and between the conductor 181 s and the spacer 143 s, and a portion of the protection layer 160 is present between the conductor 181 b and the spacer 141 b and between the conductor 181 b and the spacer 143 b.

In another aspect of the present disclosure, a semiconductor structure 100 is provided. The semiconductor structure 100 includes a substrate 110, gate structures 121 s, 121 b, 123 s, and 123 b, spacers 141 s, 141 b, 143 s, and 143 b, source/drain structures 130 s and 130 b, conductors 181 s and 181 b, and at least one protection layer 160. The gate structures 121 s, 121 b, 123 s, and 123 b are present on the substrate 110. The spacer 141 s is present on at least one sidewall of the gate structure 121 s, the spacer 143 s is present on at least one sidewall of the gate structure 123 s, the spacer 141 b is present on at least one sidewall of the gate structure 121 b, and the spacer 143 b is present on at least one sidewall of the gate structure 123 b.

The spacer 141 s has a top portion and a bottom portion between the top portion and the substrate 110. The spacer 143 s has a top portion and a bottom portion between the top portion and the substrate 110. The spacer 141 b has a top portion and a bottom portion between the top portion and the substrate 110. The spacer 143 b has a top portion and a bottom portion between the top portion and the substrate 110.

The source/drain structure 130 s is present on the substrate 110 and adjacent to the bottom portions of the spacers 141 s and 143 s, and the source/drain structure 130 s is present between the bottom portions of the spacers 141 s and 143 s. The source/drain structure 130 b is present on the substrate 110 and adjacent to the bottom portions of the spacers 141 b and 143 b, and the source/drain structure 130 b is present between the bottom portions of the spacers 141 b and 143 b. The conductor 181 s is electrically connected to the source/drain structure 130 s, and the conductor 181 b is electrically connected to the source/drain structure 130 b.

A portion of the protection layer 160 is present between the conductor 181 s and the top portion of the spacer 141 s and between the conductor 181 s and the top portion of the spacer 143 s and on the gate structures 121 s and 123 s, and a surface of the portion of the protection layer 160 facing the conductor 181 s is an outwardly curved surface. A portion of the protection layer 160 is present between the conductor 181 b and the top portion of the spacer 141 b and between the conductor 181 b and the top portion of the spacer 143 b and on the gate structures 121 b and 123 b, and a surface of the portion of the protection layer 160 facing the conductor 181 b is an outwardly curved surface.

The top portions of the spacers 141 s and 143 s have corner surfaces facing the protection layer 160 and the conductor 181 s, and the corner surfaces have a radius of curvature in a range from about 1 to about 100. The top portions of the spacers 141 b and 143 b have corner surfaces facing the protection layer 160 and the conductor 181 b, and the corner surfaces have a radius of curvature in a range from about 1 to about 200. In addition, the protection layer 160 is present between the corner surface of the top portion of the spacer 141 s and the conductor 181 s, between the corner surface of the top portion of the spacer 143 s and the conductor 181 s, between the corner surface of the top portion of the spacer 141 b and the conductor 181 b, and between the corner surface of the top portion of the spacer 143 b and the conductor 181 b.

The semiconductor structure 100 further includes a contact etch stop layer (CESL) 191. A portion of the CESL 191 is present between the conductor 181 s and the bottom portion of the spacer 141 s while absent between the portion of the protection layer 160 adjacent to the spacer 141 s and the corner surface of the top portion of the spacer 141 s. A portion of the CESL 191 is present between the conductor 181 s and the bottom portion of the spacer 143 s while absent between the portion of the protection layer 160 adjacent to the spacer 143 s and the corner surface of the top portion of the spacer 143 s. A portion of the CESL 191 is present between the conductor 181 b and the bottom portion of the spacer 141 b while absent between the portion of the protection layer 160 adjacent to the spacer 141 b and the corner surface of the top portion of the spacer 141 b. A portion of the CESL 191 is present between the conductor 181 b and the bottom portion of the spacer 143 b while absent between the portion of the protection layer 160 adjacent to the spacer 143 b and the corner surface of the top portion of the spacer 143 b.

Specifically, the protection layer 160 is made of a dielectric material, such as silicon nitride, silicon oxynitride, or combinations thereof. Embodiments of this disclosure are not limited thereto.

The semiconductor structure 100 further includes a dielectric layer 170. The dielectric layer 170 is present at least on the protection layer 160 and has openings Os and Ob at least therein. The source/drain structure 130 s is exposed through the opening Os, and at least a portion of the conductor 181 s is present in the opening Os. The source/drain structure 130 b is exposed through the opening Ob, and at least a portion of the conductor 181 b is present in the opening Ob. The conductor 181 s is electrically connected to the source/drain structure 130 s at least through the opening Os, and the conductor 181 b is electrically connected to the source/drain structure 130 b at least through the opening Ob. In addition, the protection layer 160 is absent in the openings Os and Ob of the dielectric layer 170, and the protection layer 160 is present between the dielectric layer 170 and the gate structure 121 s, between the dielectric layer 170 and the gate structure 121 b, between the dielectric layer 170 and the gate structure 123 s, and between the dielectric layer 170 and the gate structure 123 b.

The semiconductor structure 100 further includes a dielectric layer 150. A portion of the dielectric layer 150 is present between the conductor 181 s and the spacer 141 s, a portion of the dielectric layer 150 is present between the conductor 181 s and the spacer 143 s, a portion of the dielectric layer 150 is present between the conductor 181 b and the spacer 141 b, and a portion of the dielectric layer 150 is present between the conductor 181 b and the spacer 143 b. The protection layer 160 is present above the dielectric layer 150. That is, portions of the dielectric layer 150 is present between the protection layer 160 adjacent to the spacers 141 s and 143 s and the source/drain structure 130 s, and portions of the dielectric layer 150 is present between the protection layer 160 adjacent to the spacers 141 b and 143 b and the source/drain structure 130 b.

In some embodiments, the dielectric layers 150 and 170 are made of substantially the same material. In some embodiments, the protection layer 160 and the contact etch stop layer 191 are made of different materials.

The source/drain structure 130 may include at least one source/drain stressor. Embodiments of this disclosure are not limited thereto.

The protection layer 160 can protect the spacers 141 s, 141 b, 143 s, and 143 b from being over-etched during the forming the holes 171 s and 171 b. Therefore, after formation of the conductors 181 s and 181 b, the conductors 181 s and 181 b can be electrically isolated from the gate structures 121 s, 121 b, 123 s, and 123 b without causing short circuit failures and/or the leakage problem. With the protection layer 160, the device size can be further reduced without putting a heavy load on the photolithography and etching process, and thus the device performance can be improved. In addition, by corner rounding the spacers 141 s, 141 b, 143 s, and 143 b, the widths of the upper portions of the recesses 151 s and 151 b become greater, so it becomes easier to form the holes 171 s and 171 b. Therefore, the overlay and pattern loading requirements can be loosened, and the reliability and/or the yield in fabricating the semiconductor devices can be improved.

According to some embodiments of the present disclosure, a semiconductor structure includes a substrate, at least one first gate structure, at least one first spacer, at least one source/drain structure, at least one conductor, and a contact etch stop layer. The first gate structure is present on the substrate. The first spacer is present on at least one sidewall of the first gate structure, in which the first spacer has a top portion and a bottom portion between the top portion and the substrate. The source/drain structure is present adjacent to the bottom portion of the first spacer. The conductor is electrically connected to the source/drain structure. The protection layer is present at least between the conductor and the top portion of the first spacer. The contact etch stop layer is present at least partially between the conductor and the bottom portion of the first spacer while absent between the protection layer and the top portion of the first spacer.

According to some embodiments of the present disclosure, a semiconductor structure includes a substrate, at least one gate structure, at least one spacer, at least one source/drain structure, and at least one conductor. The gate structure is present on the substrate. The spacer is present on at least one sidewall of the gate structure. The source/drain structure is present on the substrate. The conductor is electrically connected to the source/drain structure, in which the spacer has a top corner surface facing the conductor, and the top corner surface has a radius of curvature in a range from about 1 to about 200.

According to some embodiments of the present disclosure, a method for manufacturing a semiconductor structure includes the following operations. A dielectric layer is formed on at least one source/drain structure adjacent to at least one spacer of at least one gate structure. An upper portion of the first dielectric layer is removed, such that the first dielectric layer and the spacer of the gate structure form a recess. A top portion of the spacer adjacent to the recess is rounded to be a rounded top corner. A protection layer is formed at least on the rounded top corner. A conductive via is formed at least through the dielectric layer to be electrically connected to the source/drain structure.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A semiconductor structure, comprising: a substrate; at least one first gate structure present on the substrate; at least one first spacer present on at least one sidewall of the first gate structure, wherein the first spacer has a first portion, a second portion, and a third portion, wherein: the second portion is between the first portion and the third portion, and the third portion is between the second portion and the substrate; at least one source/drain structure present on the substrate and laterally adjacent to the third portion of the first spacer; at least one conductor electrically connected to the source/drain structure; a protection layer overlying a top surface of the first spacer and present at least between the conductor and the first portion of the first spacer; and a contact etch stop layer present at least partially between the conductor and the second portion of the first spacer while absent between the protection layer and the first portion of the first spacer.
 2. The semiconductor structure of claim 1, wherein the top surface of the first spacer has a sigmoid curve shape.
 3. The semiconductor structure of claim 1, further comprising: at least one second gate structure present on the substrate; and at least one second spacer present on at least one sidewall of the second gate structure, wherein the source/drain structure is in contact with a sidewall of the first spacer and a sidewall of the second spacer.
 4. The semiconductor structure of claim 1, wherein the protection layer is in contact with a top surface of the contact etch stop layer and the top surface of the first spacer.
 5. The semiconductor structure of claim 1, further comprising: a first dielectric layer in contact with a sidewall of the contact etch stop layer, a top surface of the contact etch stop layer, a sidewall of the conductor, and a bottom surface of the protection layer.
 6. The semiconductor structure of claim 1, further comprising: a first dielectric layer present between the conductor and the second portion of the first spacer and between the protection layer and the source/drain structure.
 7. The semiconductor structure of claim 6, further comprising: a second dielectric layer present at least on the protection layer, the second dielectric layer having at least one opening therein, wherein at least a portion of the conductor is present in the opening.
 8. The semiconductor structure of claim 7, wherein the first dielectric layer and the second dielectric layer are made of substantially the same material.
 9. The semiconductor structure of claim 1, wherein the protection layer and the contact etch stop layer are made of different materials.
 10. A semiconductor structure, comprising: a substrate; at least one gate structure present on the substrate; a first spacer present on a first sidewall of the gate structure and a second spacer present on a second sidewall of the gate structure diametrically opposite the first spacer; at least one source/drain structure present on the substrate; and at least one conductor electrically connected to the source/drain structure, wherein: the first spacer is disposed between the conductor and the gate structure, and the first spacer has a top corner having a radius of curvature that is less than a radius of curvature of a top corner of the second spacer.
 11. The semiconductor structure of claim 10, further comprising: a protection layer present at least between a first portion of the first spacer and the conductor.
 12. The semiconductor structure of claim 11, further comprising: a contact etch stop layer present at least between the conductor and a second portion of the first spacer while absent between the protection layer and the first portion of the first spacer.
 13. The semiconductor structure of claim 12, wherein the protection layer and the contact etch stop layer are made of different materials.
 14. A semiconductor structure, comprising: a substrate; at least one gate structure present on the substrate; at least one source/drain structure present on the substrate and along a lateral pathway between a first spacer present on at least one sidewall of the gate structure and a second spacer; a protection layer overlying the gate structure and the source/drain structure; and at least one conductor electrically connected to the source/drain structure, wherein: a sidewall of the conductor is in contact with a sidewall of the protection layer, and the protection layer is spaced apart from the source/drain structure by a dielectric layer present between the first spacer and the conductor.
 15. The semiconductor structure of claim 14, wherein the first spacer is in contact with a bottom surface of the protection layer.
 16. The semiconductor structure of claim 14, further comprising: a contact etch stop layer in contact with a bottom surface of the protection layer and the sidewall of the conductor.
 17. The semiconductor structure of claim 16, wherein the contact etch stop layer is present between the conductor and the gate structure.
 18. The semiconductor structure of claim 16, wherein the dielectric layer is present between the conductor and the contact etch stop layer.
 19. The semiconductor structure of claim 18, wherein the dielectric layer is in contact with the bottom surface of the protection layer and the sidewall of the conductor.
 20. The semiconductor structure of claim 14, wherein the first spacer is in contact with a sidewall of the source/drain structure. 